This invention relates to a method in electroencephalography (class 128, subclass 2.1B) for the compression, analysis, recording and display of brain wave data. More particularly, the present invention relates to neurometrics and to the display of quantitative features extracted from the spontaneous EEG or average sensory evoked responses (AER's). The evoked responses are generated by the brain in response to a series of standardized stimulus conditions or challenges, and then averaged in such a way as to obtain an estimate of the variance at every latency point in the analysis epoch.
Although the present invention is primarily applicable to medical sciences such as neuroscience, it may also be useful for the compression, analysis, recording and display of other variable data. The data reduction and display method of the present invention produces a symbolically coded display which is intuitively natural and is easily interpreted without extensive training. The present invention is particularly applicable to an intensive electrophysiological evaluation procedure (the neurometric examination) in which a subject has presented about one hundred specified conditions or challenges which can be considered as test items. The subject's brain waves may be analyzed to produce about 400 derived measures for each of 19 brain regions for each of these conditions. Accordingly, in this type of evaluation about a half million data values may be involved, which characterize the sensory, perceptual and cognitive processes of the subject.
At the present time, it is commonplace to observe a subject's brain waves by attaching a number of removable electrodes to the subject's scalp. The subject's electroencephalogram (EEG), at the present time, is generally recorded on a paper strip chart in analog form and analyzed, on a somewhat subjective basis, by visual inspection by a trained clinical electroencephalographer who is usually a neurologist.
Electroencephalography has long recognized the need for more objective criteria for EEG diagnosis and accordingly various numerical methods have been suggested to achieve a complete and objective analysis of brain waves. Among the factors which have been suggested to be considered are frequency distribution, voltage, locus of the phenomenon, wave form, interhemispheric coherence, character of wave form occurrence, regulation of voltage and frequency and reactivity.
Some systems have been suggested to use either high speed computer computation or special electronic circuits for characterizing the extracted data. However, one major deficiency in the art is the lack of an adequate and effective method of data representation which allows the user, for example, the physician, to easily interpret and classify the subject's responses.
Bickford et al in 1971, 1973 developed a technique which he called the Compressed Spectral Array (CSA) which represents the entire electroencephalograph (EEG) report as a picture which can be viewed on a single page. The CSA divides the EEG into 4 second intervals, separates the normal from the abnormal frequencies by spectral frequency analysis, and then superimposes the smoothed curves to yield a three-dimensional display which is a function of time and frequency. These reports may be found at Electroencephalography & Clinical Neurophysiology, 1971, page 632, and Automation of Clinical Electroencephalography, Raven Press 1973, pages 55-64. Although this method permits clear visualization, it does not provide for numerical or quantitative evaluation.
Gotman et al, in Electroencephalography & Clinical Neurophysiology, 1973, 35, pages 225-235, described that the weighted ratio of the activities in various frequency bands, when multiplied by a symmetry coefficient and summed, may provide an estimate of the subject's pathology. These results were displayed as "canonograms", which are polygons of multiple rings where the number of rings is proportional to the amount of slow waves in the record. The polygons are arranged in a topographic pattern which corresponds to electrode location on the head. While this method provides for a more quantitative analysis, it still fails to provide an unequivocal numerical index of abnormality.
U.S. Pat. No. 4,037,586 to Grichnik discloses a system for EEG display in which a console having a grid of lights indicates the particular order in which the electrodes are processed. The extracted data is displayed by pen recorders.
U.S. Pat. No. 3,707,147 to Sellers discloses a method for pictorial representation of physiological responses of the patient which vary with time and position. A series of line diagrams are generated on a cathode ray tube. The potential of the extracted signal is represented on the tube by the brightness of the lines on the tube, the vertical deflection of the lines or the spacing between consecutive lines.